Footwear typically comprises an upper and a sole. The sole is the interface between the foot and the ground. Some soles have a multi-part construction that includes an outsole and a midsole. The sole generally provides traction, support and/or protection for the foot from the ground. Flip-flops or thongs refer to an open style of footwear in which a flat sole is held on the foot by a Y-shaped strap or thong that passes between the first (big) and second toes and around either side of the foot. Flip-flops can also be held to the foot with a single strap over the front of the foot rather than with a thong.
Typically, the sole of the shoe and any design included in the sole is manufactured before the shoe is assembled using steel cutting dies and die-cutting machinery that create the tread design of the sole. Sole designs can also be created through injection molding, with the assembly taking place after the production of the sole. With these methods the bottommost layer of foam or rubber has the design die cut or molded into it. Once the bottom layer has been molded, or die cut and the die cut material removed, the footwear is assembled, and the bottommost layer of the sole is adhered to the rest of the footwear.
Because of the cost of producing the steel cutting die or producing a mold for injection molding, these two production methods are cost-effective for creating large numbers of the same style of tread pattern but are typically not cost effective for generating a small number of shoes.